A wellscreen may be used on a production string in a hydrocarbon well and especially in a horizontal section of the wellbore. Typically, the wellscreen has a perforated base pipe surrounded by a screen that blocks the flow of particulates into the production string. Even though the screen may filter out particulates, some contaminants and other unwanted materials can still enter the production string.
To reduce the inflow of unwanted contaminants, operators can perform gravel packing around the wellscreen. In this procedure, gravel (e.g., sand) is placed in the annulus between wellscreen and the wellbore by pumping a slurry of liquid and gravel down a workstring and redirecting the slurry to the annulus with a crossover tool. As the gravel fills the annulus, it becomes tightly packed and acts as an additional filtering layer around the wellscreen to prevent the wellbore from collapsing and to prevent contaminants from entering the production string.
Ideally, the gravel uniformly packs around the entire length of the wellscreen, completely filling the annulus. However, during gravel packing, the slurry may become more viscous as fluid is lost into the surrounding formation and/or into the wellscreen. Sand bridges can form where the fluid loss occurs, and the sand bridges can interrupt the flow of the slurry and prevent the annulus from completely filling with gravel.
As shown in FIG. 1, for example, a wellscreen 30 is positioned in a wellbore 14 adjacent a hydrocarbon bearing formation. Gravel 13 pumped in a slurry down the production tubing 11 passes through a crossover tool 33 and fills an annulus 16 around the wellscreen 30. As the slurry flows, the formation may have an area of highly permeable material 15, which draws liquid from the slurry. In addition, fluid can pass through the wellscreen 30 into the interior of the tubular and then back up to the surface. As the slurry loses fluid at the permeable area 15 and/or the wellscreen 30, the remaining gravel may form a sand bridge 20 that can prevent further filling of the annulus 16 with gravel.
To overcome sand-bridging problems, shunt tubes have been developed to create an alternative route for gravel around areas where sand bridges may form. For example, a gravel pack apparatus 100 shown in FIGS. 2A-2B positions within a wellbore 14 and has shunt tubes 145 for creating the alternate route for slurry during the gravel pack operation. As before, the apparatus 100 can connect at its upper end to a crossover tool (33; FIG. 1), which is in turn suspended from the surface on a tubing or work string (not shown).
The apparatus 100 includes a wellscreen assembly 105 having a base pipe 110 with perforations 120 as described previously. Wound around the base pipe 110 is a wire screen 125 that allows fluid to flow therethrough while blocking particulates. The wellscreen assembly 105 can alternatively use any structure commonly used by the industry in gravel pack operations (e.g. mesh screens, packed screens, slotted or perforated liners or pipes, screened pipes, prepacked screens and/or liners, or combinations thereof).
The shunt tubes 145 are disposed on the outside of the base pipe 110 and can be secured by rings (not shown). As shown in FIG. 2A, centralizers 130 can be disposed on the outside of the base pipe 110, and a tubular shroud 135 having perforations 140 can protect the shunt tubes 145 and wellscreen 105 from damage during insertion of the apparatus 100 into the wellbore 14.
At an upper end (not shown) of the apparatus 100, each shunt tube 145 can be open to the annulus 16. Internally, each shunt 145 has a flowbore for passage of slurry, and nozzles 150 dispose at ports 147 in the sidewall of each shunt tube 145 and allow the slurry to exit the tube 145. As shown in FIG. 2C, the nozzles 150 can be placed along the shunt tube 145 so each nozzle 150 can communicate slurry from the ports 147 and into the surrounding annulus 16. As shown, the nozzles 150 are typically oriented to face an end of the wellbore's downhole end (i.e., distal from the surface) to facilitate streamlined flow of the slurry therethrough.
In operation, the apparatus 100 is lowered into the wellbore 14 on a workstring and is positioned adjacent a formation. A packer (18; FIG. 1) is set, and gravel slurry is then pumped down the workstring and out the outlet ports in the crossover tool (33; FIG. 1) to fill the annulus 16 between the wellscreen 105 and the wellbore 14. Since the shunt tubes 145 are open at their upper ends, the slurry can flow into both the shunt tubes 145 and the annulus 16, but the slurry typically stays in the annulus as the path of least resistance until a bridge is formed. As the slurry loses liquid to a high permeability portion 15 of the formation and the wellscreen 30, the gravel carried by the slurry is deposited and collects in the annulus 16 to form the gravel pack.
Should a sand bridge 20 form and prevent further filling below the bridge 20, the gravel slurry continues flowing through the shunt tubes 145, bypassing the sand bridge 20 and exiting the various nozzles 150 to finish filling annulus 16. The flow of slurry through one of the shunt tubes 145 is represented by arrow 102.
Due to pressure levels and existence of abrasive matter, the flow of slurry in the shunt tubes 145 tends to erode the nozzles 150, reducing their effectiveness and potentially damaging the tool. To reduce erosion, the nozzles 150 typically have flow inserts that use tungsten carbide or a similar erosion resistant material. The resistant insert fits inside a metallic housing, and the housing welds to the exterior of the shunt tube 145, trapping the carbide insert.
For example, FIG. 3A shows a cross-sectional view of a prior art nozzle 150 disposed on a shunt tube 145, and FIG. 3B shows a perspective and a cross-sectional view of the prior art nozzle 150. For slurry to exit the shunt tube 145, a port 147 is drilled in the side of the tube 145 typically with an angled aspect in approximate alignment with a slurry flow path 102 to facilitate streamlined flow. Like the port 147, the nozzle 150 also has an angled aspect, pointing downhole and outward away from the shunt tube 145.
A tubular carbide insert 160 of the nozzle 150 is held in alignment with the drilled port 147, and an outer jacket 165 of the nozzle 150 is attached to the shunt tube 145 with a weld 170, trapping the carbide insert 160 against the shunt tube 145 and in alignment with the drilled hole 147. The outer jacket 165 also serves to protect the carbide insert 160 from high weld temperatures, which could damage or crack the insert 160. With the insert 160 disposed in the outer jacket 165 in this manner, sand slurry exiting the tube 145 through the nozzle 150 is routed through the carbide insert 160, which is resistant to damage from the highly abrasive slurry.
The nozzle 150 and the manner of constructing it on the shunt tube 145 suffer from some drawbacks. During welding of the nozzle 150 to the shunt tube 145, the nozzle 150 can shift out of exact alignment with the drilled hole 147 in the tube 145 so that exact alignment between the nozzle 150 and the drilled hole 147 after welding is not assured. To deal with this, a piece of rod (not shown) may need to be inserted through the nozzle 150 and into the drilled hole 147 to maintain alignment during the welding. However, holding the nozzle 150 in correct alignment while welding it to the shunt tube 145 is cumbersome and requires time and a certain level of skill and experience.
In another drawback, the carbide insert 160 actually sits on the surface of the tube 145, and the hole 147 in the tube's wall is part of the exit flow path 102. Consequently, abrasive slurry passing through the hole 147 may cut through the relatively soft tube material and bypass the carbide insert 160 entirely, causing the shunt tube 145 to fail prematurely.
To address some of the drawbacks, other nozzles configurations have been disclosed in U.S. Pat. Nos. 7,373,989 and 7,597,141, which are incorporated herein by reference. U.S. Pat. Pub. No. 2008/0314588 also discloses other nozzles for shunt tubes.
Although existing nozzles may be useful and effective, the arrangements still complicate manufacture of downhole tools, alter the effective area available in the tool for design and operation, and have features prone to potential failure. Accordingly, the subject matter of the present disclosure is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.